You spend at least 80% of your time in WOW doing mundane boring shit. So I never found it to be a great game. Not just that issue, but other issues the game had.
I did raid and at a non-casual level (going for server or faction firsts) through TBC and like early WOTLK, but by mid WOTLK I had enough of it. A lot of boss patterns repeat and it really is a carrot on a stick. Once you realize that you're not really progressing and only running in place then it loses a lot of its pull. A lot of MMOers are the Spinal Tap dude arguing "But it goes up to 11!" Of course, and the monsters go up to 11 as well, and so you're not really moving the power needle, just changing the numbers on the dial range.